Pickling inhibitor



Patented Oct. 4, 1938 PICKLING INHIBITOR William P. m- Horst, PackanackLake, N. 1., as-

signor to United States Rubber Products, Inc., New York, N. Y., acorporation of Delaware No Drawing.

Serial No. 187,679

16 Claims. (c1. 148-8) of each other for thepurposes of the present in-This invention relates to the treatment of metallic surfaces where thesurface is subjected to the action of liquids of an acid nature. Moreparticularly, the invention relates to the prevention of excessivepitting, embrittlement, and undesirable dissolution of metal duringcontact with an acidic liquid. The invention also provides a picklingbath containing a new classof inhibitors; particularly for-the picklingof such as iron and steel.

It has been found that chemicals containing the thiopyrimidine ringpossess valuable inhibiting properties, that is, when added to apickling bath they greatly retard the attack of the acid on such as ironand steel without materially influencing the attack of the acid materialon scale or rust. Typical of these inhibitors are those designated asfollows: Z-mercapto tetrahydro pyrimidine (M. P. 203-4204 0.),2-mercapto-5- methyl tetrahydro pyrimidine (M. P. 217-219 0.),2-mercapto-4,6,6-trimethyl dihydro pyrimidine (M. PL 249-250 0.),2-mercapto-4,6-diethyl-6- methyl dihydro pyrimidine (M. P. 228- 230 C.)

The mercapto alkyl dihydropyrimidines may be formed by the interactionof two moles of aliphatic ketone or the equivalent thereof, with onemole of ammonium thiocyanate or with one mole of thiourea or amono-substituted thiourea, at temperatures ranging from room temperatureup to about 150 C., the preferred bodies being those prepared by the useof acetone or methyl ethyl ketone. By the equivalent of tw'o moles ofaliphatic ketone I refer to the use of one mole of a condensed ketone,such as an alkylidene ketone, which may be formed by the condensation ofone mole of a simple ketone with one or two moles of the same or adifferent ketone or of an aldehyde. The reactions by which the mercaptoalkyl dihydro pyrimidines are formed are advantageously carried out inthe presence of an excess of the ketone.

The tetrahydro pyrimidines may be prepared by the reaction of carbondisulphide on aliphatic vention.

Application January 29, 1938,

The tetrahydro mercapto bodies are believed to contain the nucleus andthe dihydro mercapto bodies are believed to contain the nucleus in whichthe neighboring C atoms have hydrogen or alkyl groups as substituents,and one of the N atoms has hydrogen or alkyl or aryl as a substituent.

In further illustration of the expanse of the invention, other ketonesmay be used for the reaction in preparation of the mercapto pyrimidines,particularly the dihydro pyrimidines,for

'example diethyl ketone, dipropyl ketone, methyl ketone, etc.

In many instances the ammonium thiocyanate may be replaced by thioureaor by a mono-substituted thioulea, such as. methyl thiourea, ethylthiourea, or phenyl thiourea.

Also

for the broad purpose of the invention various derivatives of the abovemercapto bodies may be used, namely the aldehyde and sulphurederivatives, as well as the oxidized or reduced thiopyrimidines.

Accordingly the invention broadly comprises incorporating in a usualpickling-bath,which may or may not cont any of the known in-.hibitors,-one or more of the herein referred to products of which themercapto dihydro pyrimidines are a preferred class. If desired, awetting agent may be added to improve the inhibiting properties.

When such as iron or steel is placed and kept therein for a suitablelength of time at a suitable temperature, the metal is freed from scaleand rust and after removal presents a smooth surface which can then becoated in the customary way with any protective or ornamental t ocyana3. Acid conmining25mg.oithereactionproduct Acid 25 mg. of the reactionduring a certain length of time in 750 cc. 6%- H2804 with and. withmitthe various inhibitors. at

180 F., the weights were redetermined. The lower the loss in weight, thebetter the inhibitor.

Loss in weight in mg. aiter pickling an min. min.

. Blank; no inhibitor Acid containing 25 mg. 0! the reaction product ofmethyl ethyl ketone and ammonium hi to (M P. mo-zurc oi methyl ethylketone and ammonium thlocyanate, (M. P. 29-23? 0.) plus 5% Wetanol" 3566 Acid containng 160 mg. of the on product of acetonyl acetone and ammoum thgc afate (purple powder M. P. 170- product of acetone and ammoniumthiecyanate mixed with 5% WetanoP Acid containing 25 mg.(gmZ-mercapto-S-P 217-219 0., mixed with 5% Wetanol" 7. Acid containing25 mg. oi 2-memapto-te hydro pyrimidine, mixed with 5% "W The methylethyl ketone-ammonium thiocyanate product may he prepared as follows:250 grams ammonium thiocyanate and 500 grams methyl ethyl ketone areheated on a steam bath under reflux during 24 hours. The unreactedmethyl ethyl ketone is removed by distillation. To the'residue are added1000 grams of water. The tor-insoluble terial is isolated by filtration.The yield is 143 of light-colored Powder.

Similar results may be obtained with (a) acetone-ammoniumthiocyanateproduct, which is identical with (b) the mesityl omde-ammoniumthiocyanate product and with (c) the mesityl oxide-thlourea product,which may be prepared variously as follows:

(a) 450 grams ammonium thiocyanate and 1300 grams of acetohe are heatedunder reflux on a steam bath during 84 hours. The temperature of theliquid is approximately 70 C. The

unreacted acetone is distilled ofi. To the residue, water is added andthe water-insoluble crystalline material is filtered off. The yield is18 grams of what is believed to be 2-mercapt o-4,6,6-trimethyl dihydropyrimidine, (melting at 249-250" C. after retion from alcohol or methylethyl ketone.-

(b) 18 grams ammonium thiocyanate and 25 grams mesityl omde are heatedduring 8 hours at C. The contents of the reaction vessel are poured intowater and the water insoluble materlal is filtered ed. The yield is 23grams of reaction product.

(c) 985 grams thiourea and 1300 grams mesityl omde are heated .underreflux during 24 hours. The mesityl oxide is removed by distillation.mrisidueistreatedwrthwatertoremove w o: thiourea. The crudewater-insoiuhl amountstoaboutmgramsilid. E7 n x a: hon: melting be usedinstead, for example those obtained from sulfite pulp liquors, e. g.lignin sulfonates, etc.

In preparing the thio-pyrimidines, the time and temperature of thereaction and the amount of reactants may be varied, as is foundsuitable. 5 Also a catalyst may or may not be used as desired, toregulate the reaction. The inhibitors may he used as such or mixed withother chemicals. Also the thiopyrimidines of this invention maybe madeby any of the methods known to the art.

Instead of using single acids, a mixture of acids may be used, forexample, a mixture of hydrociiiloric and sulphuric acids, in thepickling opera on.

The chemicals disclosed herein may be used in the pickling of steel, inacids used for cleaning equipment, or metal articles in general, in acidsolutions to be circulated or distributed through metallic pipingsystems, in acid reaction mixtures in order to protect chemical reactionvessels, or in hydrochloric acid used in the mining industries.Furthermore, the inhibitors may be added to concentrated acid solutionswithout undergoing any substantial impairment of their inhibiting power.

With the detailed description given above, it will be clear variouschanges may be made without departing from the principle of theinvention, for instance the bath need not necessarily be what is knownas a pickling bath but may be used in connection with any conditionwhere metal would be attacked by acid liquids, and the inventionis notto be limited except as indicated in the appended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith which comprises adding to said acid solution a mercaptopyrimidine compound.

2. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith which comprises adding to said acid solution analkyl-substituted mercapto pyrimidine.

3. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by acids which comprises treatingthe metal with an acid solution containing an alkylsubstituted dihydromercapto pyrimidine.

4. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by acids which comprises treatingthe metal with an acid solution containing a 2-mercapto-4,6,6-trialkyldihydro pyrimidine.

5. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith which comprises adding to said acid solution a productobtainable by the reaction of carbon disulphide with an aliphatic 1,3diamine. Y

6. A process of protecting a metal surface such as iron, steel or thelike against undesirable disso- 05 lution by acids which comprisestreating the metal with an acid solution containing alkyl-substitutedtetrahydro mercapto pyrimidine.

7. A prom of protecting a metal surface such asiron, steel or the likeagainst undesirable dissolution by an acid solution in contacttherewith, which comprises adding to said acid solution a productobtainable-by the reaction of an aliphatic ketone with ammoniumthiocyanate.

8. Aprocess of protecting a metal surface such '15 15 7 productobtainable bythe reaction of acetone and as iron, steel or the likeagainst undesirable dissolution by an acid solution in contacttherewith, which comprises adding to said acid solution a productobtainable by the reaction of a dialkyl ketone compound with ammoniumthiocyanate.

9. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith. which comprises adding to said acid solution a productobtainable by the reaction of methyl ethyl ketone and ammoniumthiocyanate.

10. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith, which comprises adding to said acid solution a ammoniumthiocyanate.

11. A pickling bath for iron and steel products comprising a picklingacid and a mercapto pyrimidine compound.

12. A pickling bath for iron and steel products comprising a picklingacid and a product ohtainable by the reaction 0! an aliphatic -ketonewith ammonium thiocyanate.

13. A pickling bath for iron and steel products comprising a picklingacid and a product obtainable by the reaction of acetone with ammoniumthiocyanate. v

14. A process of protecting a metal surface such as iron, steel or thelike against undesirable dissolution by an acid solution in contacttherewith which comprises adding to said acid solution a productobtainable by the reaction of an aliphatic ketonewith a thiourea.

15. A pickling bath for iron and steel products comprising a picklingacid and a product obtainable by the reaction of carbon disulphide withan aliphatic 1,3 diamine.

16. A pickling bath for iron and steel products comprising a picklingacid and a product obtain-

